Dynamic random access memory (DRAM), such as found in computers, is used to store binary data. Each location or "cell" of DRAM holds a single "bit" of information, which may have a value of "1" or "0". In each memory cell, this value is represented by the presence or absence of charge on a capacitor. When a DRAM power supply is first turned on or initialized, the plate electrodes of these capacitors are maintained at electrical ground for a short time until the power supply has stabilized. The plate electrodes are then precharged to a predetermined voltage by a voltage generator.
An example of this conventional technique is illustrated in FIG. 1. Conventional circuit 10 includes cell plate voltage generator 12 having an output voltage at node A; switching transistors MN1 and MP1 for connecting and disconnecting the output voltage of voltage generator 12 to and from terminal Vcp, which is connected to the cell plate; switching transistor MN2 for grounding the Vcp terminal; and a signal P-U which activates and deactivates switches MN1, MP1 and MN2.
FIG. 2 is a timing chart which illustrates the operation of conventional circuit 10. After the power supply (shown in FIG. 2 as signal P) is first turned on and has stabilized, signal P-U shifts to a high level. When signal P-U goes high, it turns off transistors MN1 and MP1, thereby isolating node A and terminal Vcp from each other. At the same time, terminal Vcp is coupled to ground by the activation of switching transistor MN2. After a brief time (such as to allow establishment of a back bias voltage), the signal P-U returns to low, thereby activating switching transistors MN1 and MP1 to couple voltage generator 12 to terminal Vcp.
To increase DRAM capacity, one needs to use more cells. This in turn increases the overall capacitance of the plate electrodes. In order to continue charging these larger numbers of plate electrodes in a very short period of time, it is necessary to use a more powerful voltage generator having a larger current driving capacity. Unfortunately, these large capacity generators are continuously operated, even during standby periods. As a result, power losses reach unacceptable levels.